Mars has long occupied a central place in scientific and cultural imaginations as the nearby world most plausibly capable of hosting life. This article traces the intellectual and institutional evolution of astrobiology from its origins as NASA-supported exobiology through the Viking missions and into the contemporary framework that guides life-detection efforts today. We examine the oscillation between optimism and pessimism that characterized scientific views of Martian life in the decades preceding Viking, shaped by laboratory experiments, telescopic observations, early spacecraft encounters, and evolving hypotheses of planetary environments. Key figures, including Joshua Lederberg, Carl Sagan, and James Lovelock, advanced contrasting visions of how life might manifest beyond Earth and how it should be detected. Results from Mariner and Viking missions revealed Mars to be both more alien and more complex than previously assumed, underscoring the dangers of limited data and Earth-centric assumptions. In hindsight, Viking's ambiguous biological results highlighted the necessity of grounding life-detection experiments in a robust understanding of planetary context, comparative planetology, and the diversity of life on Earth. We argue that Viking's greatest legacy lies not in definitive answers but in establishing methodological and epistemological foundations that now inform biosignature standards, life-detection frameworks, and future exploration of Mars, ocean worlds, and exoplanets.
Grinspoon et al. (Wed,) studied this question.